Even if the money were available, no one had developed or even proposed a levee system big enough to prevent this.
I have a friend who lives in NO and thank heavens evacuated, and he says even the locals all it "Bienville's Mistake". You can't protect a city built 6-8 feet below sea level forever. I used to inspect levee like structures and small earthen dams, and the worst case scenario is that once one goes the others get undercut and start to fail. If there is a 200 foot section missing somewhere I would expect a much larger failure is a possibility. This is going to be a catastrophe of monumental proportions for that area and a monetary disaster for all of us.